This invention relates to systems for automatic or computer-controlled manipulation of sheet material during processing, e.g., fabric or other limp material to be assembled at a sewing station.
During the construction of a useful item from raw stock of flat goods (e.g., cloth, paper, plastic, and film), it is often necessary to precisely position and guide the flat goods through a work station. Typical work stations perform assembly operations such as joining, cutting or folding. For example, such work stations can be equipped with sewing machines for joining multiple layers of limp fabric, such as may be from separate limp material segments, or from several regions of the same (folded) limp material segment.
Conventionally, the positioning and guiding of the fabric-to-be-joined is accomplished by skilled human operators. The operators manually feed or advance the fabric-to-be-joined through the stitch forming mechanism of the sewing machine along predetermined seam trajectories on the fabric. The resultant seams can be straight or curved, or a combination of both as is often required in the assembly of fabric panels to form articles of clothing, for example. Typically, the fabric-to-be-joined must be precisely positioned and accurately directed to the sewing head to achieve the desired seam. The human operator must therefore function not only as a "manipulator" of the fabric but also as a real-time "sensing and feedback medium", making small adjustments, e.g., in orientation, fit-up and seam trajectory, to obtain quality finished goods. The adjustments are required, for example, due to variations in seam type, geometry, location and fit-up.
There are many forms of seams that are conventionally formed, such as superimposed seams, lapped seams, bound seams, and edge finishing seams. Such seams are described generally in "The Technology of Thread and Seams", J&P Coats Limited, Glasgow, Scotland (undated), pages 74-79.
One form of seam which is required in the fabrication of certain articles is the so-called full felled or double lapped seam. The full felled seam is typically used to join one lateral edge of each of two limp material segments. In that seam, the edges to be joined are folded over in an interlocking relationship (where their cross-sections form interleaved opposed V's or C's) and then one or two rows of stitches are established along the principal axis of the seam through all four layers of the interlocked segments.
In the prior art, to assist in the formation of such a seam, an operator manually presents and feeds two limp material segments to be joined to a fold assembly coupled to a sewing machine. The fold assembly, for example, a Simanco USA model 230056, is adapted to receive the presented segments and to guide the edges so that at the output end of the fold assembly, the two segments emerge with their lateral edges interlocked and ready for joining. The fold assembly is positioned so that the emerging segments are driven by the feed dogs of the sewing machine to the needle and bobbin assembly of the sewing head of the machine.
One drawback of this technique is that it is labor intensive; that is, a large portion of the cost for manufacture is attributable to manual labor. One of the further problems of the prior art seam forming techniques lies with the conventional fold assembly. With such an assembly, the formation of straight seams is fairly effective, although considerable manual assistance is required. However, the formation of a curved felled seam is extremely difficult, due to bunching of the limp material segments as they are fed to and drawn through the fold assembly.
To reduce labor cost in the clothing assembly industry, automated or computer-controlled manufacturing techniques have been developed for many of the desired assembly operations. However, there have not been any effective techniques developed for the automated formation of high quality full felled seams. Moreover, even the manual assisted techniques have limited effectiveness due to the required degree of human intervention and are limited in their ability to accommodate curved seams.
Accordingly, it is an object of the invention to provide an improved method and apparatus for positioning and guiding sheet material, e.g., fabric or other limp material to be processed, in the formation of seams.
It is another object of the present invention to provide an improved flat-material manipulation device suitable for automatic or computer-controlled seam forming operations, which is of simple, rugged, versatile, and economical design.